1. Field of the Invention
The present invention relates to an illuminant for a discharge lamp, and in particular, to an illuminant for a discharge lamp which has simple structure, which lends itself to mass production, and which exhibits superior durability.
2. Description of the Related Art
Discharge lamps with high illumination efficiency are widely employed for general household or business use, as street lamps, as wall projection lamps, as lamps for advertisement or for illumination, in automobiles, and in cinematographs or projectors. In these various types of discharge lamps, discharge electrodes are placed to oppose each other in a discharge chamber filled with a discharge gas, and illumination effect is obtained by applying a predetermined voltage between the discharge electrodes to dissociate the discharge gas. Various illumination luminance and illumination colors or the like can be created by selecting the discharge gas employed, the pressure in the discharge chamber, or other characteristics.
Common discharge lamps have a structure wherein an illuminant is stored in an external glass tube, the open end of which is generally sealed by a socket for connecting a power source. Conventional illuminants require a complicated structure in order to obtain desired discharge characteristics and, thus, are not suited to mass-production. Consequently, there has been a problem that illuminants tend to be expensive. Moreover, while high durability is desired for a discharge lamp, a conventional discharge lamp has a tendency to easily be broken due to external impact or thermal load during use.
As a structure for such a conventional illuminant, an illuminant for a metal halide lamp which is one type of a discharge lamp is disclosed in Japanese Patent Laid-Open Publication No. Hei 5-217555. In this conventional apparatus, a pair of electrodes are inserted into a quartz illumination tube and the sealed discharge space section is filled with a predetermined amount of mercury, sodium iodide, scandium iodide, or the like, along with xenon which acts as the starting gas. Sealing sections are joined at both ends of the discharge space section. The electrodes and external lead lines are connected via metal foils provided on the sealing sections.
In this type of illuminant, there has been problems in that it is difficult to place the electrodes to oppose each other within the illumination tube at predetermined positions and that the positions of the electrodes in the tube change when both ends of the quartz illumination tube are pinch processed by heating the tube. Moreover, the junction between the discharge space section and sealing section requires complicated heat fusion steps, and therefore, various problems are also present in view of mass-productivity and durability.
In particular, the positional deviation of the opposing electrodes within the illuminant causes a problem that a desired focusing effect cannot be obtained due to the deviation of the position of the illumination source from a defined value when the discharge lamp is used as an automobile lamp, or a lamp for a cinematograph or for a projector.